A. Field of the Invention
This invention relates to the can manufacturing art, and more particularly to a novel construction and arrangement of the joint or seam which connects a can body to a can end, and to a method of affixing a can body to a can end.
B. Description of Related Art
It is well known to draw and iron a sheet metal blank to make a thin-walled can body for packaging beverages, such as beer, fruit juice or carbonated beverages. In a typical manufacturing method for making a drawn and ironed can body, a circular disk or blank is cut from a sheet of light gauge metal (such as aluminum). The blank is then drawn into a shallow cup using a cup former. The cup is then transferred to a body maker where the can shape is formed. The body maker re-draws and irons the sidewall of the cup to approximately the desired height, and forms dome and other features on the bottom of the can.
Can body manufacturing techniques are described in the patent literature. Representative patents include U.S. Pat. Nos. 6,305,210; 6,132,155; 6,079,244; 5,984,604, and 5,934,127, the contents of which are incorporated by reference herein. Domer assemblies for drawing and ironing machines are described in U.S. Pat. Nos. 4,179,909; 4,620,434; 4,298,014, all assigned to National Can Corporation, the contents of which are incorporated by reference herein.
In current practice, after the can is formed in the body maker, the can is sent to a separate necking and flanging station, where neck and flange features are formed on the upper region of the can. The flange is used as an attachment feature for permitting the lid for the can, known as an “end” in the art, to be seamed to the can. The last station in the necker-flanger is a reformer station. This station includes a set of tools for reforming the bottom profile of the can in order to increase the strength of the bottom profile. U.S. Pat. Nos. 5,222,385 and 5,697,242, both assigned to American National Can Co., describe a can body reforming apparatus and methods for reforming can bodies to increase the strength of the bottom profile. After necking, flanging and bottom reforming, the top edge of the can is trimmed and the can is ready to be shipped to the location of filling the can and attachment of the can end.
Can ends are subject to a separate manufacturing process. U.S. Pat. No. 6,533,518 and references cited therein describe several press designs used to form a can end from a sheet of end material.
At the time of filling the can with product, the end is placed over the can body and then attached to the can using a process known as seaming. FIGS. 1A and 1B are cross-sections showing a can end 10, can body 14, seam tooling comprising chuck 16 and seaming rollers 18 and 22, showing the flange 20 of the can body 14 and the curl 12 of the can end 10 before (FIG. 1A) and after (FIG. 1B) a double seaming operation, in accordance with a prior art double seam joint. The can end 10 has a peripheral curl 12 which is rolled against a peripheral flange 20 in the can body 14. The can end 10 is placed on top of the can body 14 and a seaming chuck 16 is inserted into the can end 10. A first roller 18 (FIG. 1A) is moved laterally into engagement with the curl 12 and presses the curl 12 against the flange 20 in a first seaming operation. In a second seaming operation, as shown in FIG. 1B, as second seaming roller 22 continues the seaming operation and presses the flange 20 and curl 12 together against the seaming chuck 16 to form a tight double seam joint 24 between the can end and the can body, as shown.
The art has proposed joining the can end to the can body using a combination of a rolling action and a laser weld which welds the can end and can body together in the area of the seam. See, for example, published PCT application of Williamson, publication no. WO 02/42196, the content of which is incorporated by reference. See also U.S. Pat. Nos. 5,186,592; 5,125,780 and 4,854,467 to Budenbender; U.S. Pat. No. 4,738,560 to Brussow, and U.S. Pat. No. 4,758,704 to Kogel, all incorporated by reference herein.
The potential for using a laser, in conjunction with a roller seam, offers the potential for a can and can body to be constructed using less metal for the same volume than that used in current practice. In particular, the laser seam approach may permit the can end to be joined to the can body in a single seam, which requires less metal in the peripheral curl of the can end and in the flange of the can body, whereas the current approach using a double seam (FIGS. 1A and 1B) requires more metal in the peripheral curl of the can end and in the flange of the can body. The prospect of laser seaming also has the potential for elimination of the application of a seam compound to the peripheral channel in the end, which seals the end can when the double seam is formed.
Despite the potential for metal utilization savings and elimination of joint compound, laser seaming has yet to be practiced in the beverage can art in this country. One concern with laser seaming with a single seam (as proposed in Williamson) is whether the seam design is sufficiently strong such that it will allow cans to be pressurized to 90 PSI or greater, which is currently a design standard for can designs in the beverage industry. There is a need for improvements in seam designs that provide for increased strength in the seam. This invention meets that need. It also provides improvements in seam designs that are particularly useful in combination with laser welding of the seam to increase the strength of the seam.